Deck Advice Requested

[tealetm]

Let me start off by saying I both understand this isn't a deck building forum, nor are most of you structural engineers. With that said, I'd solicited a lot of good advice here previously when building my garage/barn so I figured I'd come back and pick your brains on this.

I have a log cabin, which had a deck on it which we just tore off due to deterioration.

We have existing concrete piers 6' from the foundation wall (48" depth), spaced at approx 8' on center and will be reusing them as they are very sound. We would like the deck to be at least 8' in width from the cabin, which would be a 6' span to the piers with a 2' canteliever. Decking will be 2x4 PT at a 45deg angle to the joists (to match an existing adjacent deck).

My questions are:

-what size PT joists would you use at 16" on center?
-what size laminated 2x PT beam would you use?

Does anything else look wrong to you?

Thanks for the input!

 

[billconner]

Only guessing from memory because on a plane and can't get to documents. I sure think 2x6 joists and probably a double 2x8 beam. Careful with ledger - that's involved in most dec failures.

 

[cgrutt]

Not a pro but I'd use min 2x10 (2) for beam (spanning 8' if I understand you correctly). I would notch beam into your 6x6 posts and through bolt. You could probably get away with 2x6 joists but I would use min 2x8 if it were mine.

 

[mike93lx]

Look up the awc deck guide. It has all your answers and is a great reference

 

[58Yeoman]

Take this for what it's worth. We bought our house in 2008 and it had a ground level deck that was in bad shape. I demo'd it and Lowe's had a couple guys come and build a new deck, but not to my specs. I couldn't live with it, so I called Lowe's within the year and they came back with a real crew. This crew said that the ledger was a no-no and removed it and built the deck correctly. I don't remember if the original deck had a ledger or not, but I'm thinking not because the house is brick, and I would remember taking off brick.

 

[tarmy]

I used 2x8 for joists and 4x8 for support. I am not a fan of sistering 2x for anything.

 

[CN Spots]

^ I haven't seen a state park that looked that nice.

 

[sjvicker]

Read up on the 25% or 1/4 rule for deck overhangs. Some areas only allow the overhang to be 25% of the main joist span. This is 18" in your case.

 

[billconner]

Look up the awc deck guide. It has all your answers and is a great reference

This is best answer. And ledger is weakest point. I am also a big advocate for using the joist tape.

If your using joist hangers, I'm curious if you use screws or nails, and stainless steel or galvanized. I'm leaning towards galvanized screws - Simpson Strong tie - but it is a porch with roof so more damp than wet. If an unroofed deck, I think I'd go SS.

 

[billconner]

Read up on the 25% or 1/4 rule for deck overhangs. Some areas only allow the overhang to be 25% of the main joist span. This is 18" in your case.

wouldn't be 25% if allowable deck span, not what you did? I'm using 2x6 on 16" centers and iirc 2x6 is a little over 8' span, and this 2' cantilever. Pretty basic engineering - cantilever is third of simple beam.

 

[sjvicker]

wouldn't be 25% if allowable deck span, not what you did? I'm using 2x6 on 16" centers and iirc 2x6 is a little over 8' span, and this 2' cantilever. Pretty basic engineering - cantilever is third of simple beam.

I understand this as 25% of joists actual span and not 25% of allowable span. I could definitely be wrong here as on google I can find answers to support this both ways.

 

[Dodgeboy2020]

Just one thought, I know you mentioned using 2x decking material but if you're considering using any of the composite materials down the road they don't do so well with 16" OC structure on a diagonal, most manufacturers recommend 12" OC for that application. Again probably not applicable in this situation but just wanted to put it out there if someone else is reading thru this.

 

[Viper98912]

Use the deck designer on Lowe's website

 

[cgrutt]

Look up the awc deck guide. It has all your answers and is a great reference

Great reference. Curious how far off my "gut" response was. 2x10(2) beam w/ 8' span, notched and through bolted to 6x6 posts. 2x8 joists 16 o/c with 2' cantilevere. Just for S&G.

 

[JSutter]

https://content.civicplus.com/api/assets/b5d0d850-71c2-43db-a8c4-e1e0a7f4c79a?cache=1800

2015 IRC, anyone have a newer version?

 

[billconner]

2x6 work fine for joist spans. Might want a triple 2x8 or double 2x10 beam. A double 2x8 probably works, but very close.

 

[Jackfre]

Your drawing of the attachment to the house will deteriorate the siding over time. I just finished my version of the PO Blues where I had to cut off the joists, repair the siding and rim joist. Look up some drawings of ledger boards and make your choice. In my case I cut back the joists, after removing the 2x10 which attached to the house. For the repair I had some 24 ga flashing fabbed up. Could have been done with Z-flashing but this worked out well.

 

[JSutter]

Maine Deck Brackets are a great alternative to ledger boards attached directly to the building.

Maine Building Materials; The Maine Deck Bracket Company

We manufacture brackets for attaching Decks, Stairs, Signs and other appendages to buildings

deckbracket.com

There's also ledger spacers such as Deck2Wall.

 

[tarmy]

This here is how I attached the deck. The 2x12 is flashed and bolted to the rim joist in the house. the outer board 2x8 is lagged into the 2x12 with those 1/2’ plastic spacers mentioned above. The key to this is the correct flashing above, behind and sealed so that all the water/ice drains properly.

 

[billconner]

The foolproof way is don't attach to house. Posts and a beam. Also gets around footings at frost depth. Small footings in the ground rather than 4' deep here.

 

[tealetm]

Thank you all. I like the idea of the spacers between the ledger and the house and I have a good idea on joist/beam sizing now.